Zellweger spectrum disorder

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Zellweger spectrum disorder is a condition that affects many parts of the body. Cases of Zellweger spectrum disorder are often categorizes as severe, intermediate, or mild.

Individuals with severe Zellweger spectrum disorder usually have signs and symptoms at birth, which worsen over time. These infants experience weak muscle tone (hypotonia), feeding problems, hearing and vision loss, and seizures. These problems are caused by reduced myelin, which is the covering that protects nerves and promotes the efficient transmission of nerve impulses. The part of the brain and spinal cord that contains myelin is called white matter. Reduced myelin (demyelination) leads to loss of white matter (leukodystrophy).

Children with severe Zellweger spectrum disorder also develop life-threatening problems in other organs and tissues, such as the liver, heart, and kidneys, and their liver or spleen may be enlarged. They may have skeletal abnormalities, including a large space between the bones of the skull (fontanelles) and characteristic bone spots known as chondrodysplasia punctata that can be seen on x-ray. Affected individuals can have eye abnormalities, including clouding of the lenses of the eyes (cataracts) or involuntary, side-to-side movements of the eyes (nystagmus). Severe Zellweger spectrum disorder involves distinctive facial features, including a flattened face, broad nasal bridge, high forehead, and widely spaced eyes (hypertelorism). Children with severe Zellweger spectrum disorder typically do not survive beyond the first year of life.

People with intermediate or mild Zellweger spectrum disorder have more variable features that progress more slowly than those with the severe form. Affected children usually do not develop signs and symptoms of the disease until late infancy or early childhood. Children with these intermediate and mild forms often have hypotonia, vision problems, hearing loss, liver dysfunction, developmental delay, and some degree of intellectual disability. Most people with the intermediate form survive into childhood, and those with the mild form may reach adulthood. In rare cases, individuals at the mildest end of the condition spectrum have developmental delay in childhood and hearing loss or vision problems beginning in adulthood and do not develop the other features of this disorder.

The severe, intermediate, and mild forms of Zellweger spectrum disorder were once thought to be distinct disorders. The severe form was known as Zellweger syndrome, the intermediate form was neonatal adrenoleukodystrophy (NALD), and the mild form was infantile Refsum disease. These conditions were renamed as a single condition when they were found to be part of the same condition spectrum.

Inheritance

From: MedlinePlus Genetics, National Library of Medicine

Autosomal recessive

Understanding terms used in the source

These definitions explain medical words used above. A definition is not evidence that another condition is present, and it does not predict how a symptom will develop. Ask the clinician which terms apply to the actual examination or test result.

Intellectual disability

The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence.

Leukodystrophy

Leukodystrophy refers to deterioration of white matter of the brain resulting from degeneration of myelin sheaths in the CNS. Their basic defect is directly related to the synthesis and maintenance of myelin membranes. Symmetric white matter involvement at MRI is a typical finding in patients with leukodystrophies.

Hypertelorism

Interpupillary distance more than 2 SD above the mean (alternatively, the appearance of an increased interpupillary distance or widely spaced eyes).

Hypotonia

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

Nystagmus

Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms.

When it may begin

From: MedlinePlus Genetics, National Library of Medicine

Individuals with severe Zellweger spectrum disorder usually have signs and symptoms at birth, which worsen over time. These infants experience weak muscle tone (hypotonia), feeding problems, hearing and vision loss, and seizures. Affected children usually do not develop signs and symptoms of the disease until late infancy or early childhood. Most people with the intermediate form survive into childhood, and those with the mild form may reach adulthood. In rare cases, individuals at the mildest end of the condition spectrum have developmental delay in childhood and hearing loss or vision problems beginning in adulthood and do not develop the other features of this disorder.

Inheritance in the source

From: MedlinePlus Genetics, National Library of Medicine

Autosomal recessive

Understanding the inheritance label

From: MedlinePlus Genetics

An autosomal recessive pattern usually involves disease-causing changes in both copies of a gene. Parents may each carry one altered copy without having the condition themselves. A genetic counsellor can explain carrier testing and reproductive implications using the actual laboratory findings, rather than the condition name alone.

Which doctor should you see?

The suggested department for discussing Zellweger spectrum disorder is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Zellweger spectrum disorder. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.